A styrene-based thermoplastic resin is a resin synthesized by homo-polymerizing styrene as a main raw material or co-polymerizing it with monomers to obtain advantages from the properties of each monomer. As the styrene-based resin, there are general purpose polystyrene (GPPS) resins and expendable polystyrene (EPS) resins obtained by homopolymerizing styrene, high-impact polystyrene (HIPS) resins being copolymers of styrene and butadiene rubber, and ABS resins obtained by grafting styrene and acrylonitrile to a butadiene rubber.
In addition, there are ASA resins obtained by co-polymerizing styrene and acrylonitrile with an acrylic rubber as a base, MBS-based impact-reinforcing agents obtained by co-polymerizing styrene and methyl methacrylate (MMA) with polybutadiene as a base, or acrylic-based impact-reinforcing agents obtained by co-polymerizing methyl methacrylate (MMA) and an acrylate monomer with an acrylic rubber as a base. Styrene has an advantage in processability, butadiene has an advantage in impact resistance, and acrylonitrile has advantages in rigidity and chemical resistance.
Styrene-based thermoplastic resin compositions are utilized in various applications. ABS resins represented by rubber-reinforced styrene-based resins are widely used in electric and electronic components, office appliances, automotive components, etc. due to their excellent mechanical properties, molding processability, and the like. In particular, since the temperature inside an automobile is raised due to heat generated in the engine and heat due to sunlight exposure from the outdoors, a heat-resistant ABS resin is generally used as the ABS resin used for automotive components.
General methods to render the ABS resin heat-resistant include a method of adding α-methylstyrene (AMS)-based or maleimide-based monomers, which have excellent heat resistance, in the ABS polymerization procedure, and a method of mixing the heat-resistant copolymer comprising the above monomers having excellent heat resistance with the ABS resin. However, such a heat-resistant ABS resin has lower fluidity compared to general-purpose ABS resins, and thus it has a limitation in manufacturing large parts or parts with complicated structure by injection. It also causes a problem of quality and deformation in the appearance of the molded article.
To solve the problem of flowability in such a heat-resistant ABS resin, a method for improving the flowability by using a phosphoric ester compound is known, but there is still the remaining problem wherein the heat resistance is significantly lowered in the resin composition using the phosphoric ester compound, and the so-called “juicing phenomenon” is caused, in which the phosphoric ester compound is volatilized during the molding to be deposited on the surface of the molded article.